SAE TECHNICAL
`PAPER SERIES
`
`2002-01-0285
`
`Diesel Emission Control: 2001 in Review
`
`Timothy V. Johnson
`Corning Incorporated
`
`Reprinted From: Diesel Exhaust Emissions Control 2002:
`SCR, HC, DeNOx, and Measurement
`(SP–1674)
`
`400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A.
`
`Tel: (724) 776-4841 Fax: (724) 776-5760
`
`SAE 2002 World Congress
`Detroit, Michigan
`March 4-7, 2002
`
`BASF-2028.001
`
`

`
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`ISSN 0148-7191
`Copyright 2002 Society of Automotive Engineers, Inc.
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`Printed in USA
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`BASF-2028.002
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`

`
`2002-01-0285
`Diesel Emission Control: 2001 in Review
`
`Timothy V. Johnson
`Corning Incorporated
`
`Copyright © 2002 Society of Automotive Engineers, Inc.
`
`ABSTRACT
`
`The paper covers reported developments from all major
`conferences in the year 2001 that occurred in the US and
`Europe and gives a comprehensive overview of the current
`state-of-the-art in diesel emission control.
`
`The latest developments on nature of diesel particulates
`are summarized. The variety of diesel particulate filter
`regeneration strategies that will become so important to
`filter application are reviewed. Filter retrofit and durability
`issues are addressed. DeNOx catalysts, SCR, NOx traps
`for diesel, and non-thermal plasma methods are
`summarized. Integrated NOx/PM systems are described.
`NOx efficiency and fuel penalty costs for various NOx
`systems are summarized, as are the published capital
`costs of some key systems.
`
`INTRODUCTION
`
`The field of emission control for diesel engines is certainly
`active and
`rapidly evolving.
` The development of
`technology and fundamental understanding is generally
`regulation driven, although commercial and green
`marketing interests are becoming a much greater influence
`than even a couple years ago. The latter trend is most
`evident with the introduction of diesel particulate filters on
`European diesel passenger cars in June 2000 (Peugeot)
`and
`the subsequent propagation of
`the
`technology.
`However, the heavy-duty sector is also moving in this
`direction, with
`filter-equipped school buses becoming
`available to a limited extent in the US in 2001, and some
`filter-equipped
`trucks emerging
`in
`the European
`marketplace, about 4 years earlier than required.
`
`Regarding the fundamental driver of emission control
`technologies, regulations, and the interplay of the two, the
`reader is referred to discussion on this point in reference 1
`for assessment of the light-duty sector. The European and
`US light-duty diesel regulations have not changed since
`then. In summary, the Euro IV regulations coming in 2005
`are tight enough to force either filters or about 40% efficient
`NOx emission control equipment only on vehicles weighing
`more than about 1700 kg (3700 lbs.). The market appears
`to be moving to filters to meet this requirement.
`
`It is much more complicated in the US, where the light-duty
`Tier 2 regulations begin phasing-in with MY2004. At that
`time, vehicles of a gross vehicle weight of more than 6000
`pounds (2730 kg) can emit no more than 0.6 g/mile NOx
`(60% tightening from Tier 1) and 0.08 g/mile PM. Although
`these PM levels are roughly double those of Euro IV and
`the NOx is 50% higher, these are caps and the required
`fleet average NOx for the heavier vehicles is about half that
`of Euro IV. This imparts a degree of strategy in the US
`fleet emissions balance. For example, for every heavier
`diesel sold (>6000 lbs.) at the cap by a manufacturer, about
`three “Bin 5” vehicles (<0.07 g/mile NOx) in the same
`weight class will be needed to hit the fleet average. Given
`low penetration of diesel vehicles in the US in this
`timeframe this might not be a problem, and diesel oxidation
`catalysts plus new engine technologies appear to suffice to
`keep heavy diesels under the cap. The picture markedly
`changes in MY2008, when the cap in these vehicles
`tightens to 0.2 g/mile NOx (50% tighter than Euro IV) and
`0.02 g/mile PM, and the required fleet average phases to
`0.07 g/mile NOx, or about 80% tighter than Euro IV. Ultra-
`low sulfur diesel (ULSD) fuel of less than 15 ppm sulfur will
`be widely available to enable lean NOx traps (LNT), in
`addition to the selective catalytic reduction (SCR) option,
`and diesel particulate filters (DPF). The development of
`these technologies, plus the movement towards similar
`fuels in Europe, will certainly influence the levels of diesel
`tailpipe regulations in Euro V, expected to be promulgated
`in 2010. As such, work on LNT, SCR, and DPFs for light-
`duty applications is quite active.
`
`On the heavy-duty side, the US2004 regulations for diesel
`trucks is coming due for the vast majority of suppliers in
`October 2002. The NOx cap of about 2.0 g/hp-hr (NOx
`plus hydrocarbons of 2.4 g/bhp-hr) is forcing the use of
`exhaust gas
`recirculation
`(EGR), which generally
`decreases the peak flame temperatures in the cylinder.
`NOx reductions of up to 60% at some load points is
`realized. Particulates go up with EGR, and depending on
`engine and EGR technology, may or may not require a
`diesel oxidation catalyst (DOC) to take down the soluble
`organic fraction (SOF) of the PM. As the emission is
`expressed in terms of NOx+HC (hydrocarbons), DOCs are
`also of interest to drop hydrocarbons.
`
`BASF-2028.003
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`In Europe, the Euro IV regulations come next, in 2005.
`Although the NOx cap is about 30% higher than US2004,
`the PM regulation is nominally 75 to 85% tighter. The
`approach to this challenge is interesting. The combination
`of engine technologies (excluding EGR) plus SCR NOx
`control (no filters) is allowing engines to be run at high NOx
`and low enough PM to hit the Euro IV regulations.
`(Nominally, 55 to 65% NOx efficiency is needed to hit the
`regulation.) In this operating mode diesel fuel consumption
`is dropped upwards of 7 to 10% from the Euro III baseline
`(2). Indeed, a European consortium (KfZ-Entstickung) is
`making significant progress in moving the infrastructure
`towards urea distribution to enable SCR. An option
`emerging for urban heavy-duty vehicles is to employ EGR
`and particulate filters. SCR is potentially troublesome at
`the low exhaust temperatures in these applications. In
`addition, SCR does little or nothing to reduce nanoparticles
`(3), which is becoming perhaps the most important health
`issue facing the industry. As such, there is interest in using
`filters on urban vehicles.
`
`Next in line for tightening on the heavy-duty side are US
`trucks with the 2007 Diesel Rule, followed closely by
`European trucks, with the so-called Euro V regulation in
`2008.
` The option
`in
`the 2007 Diesel Rule
`that
`manufacturers appear to be employing is to sell 100% of
`their engines at a 1.1 g/bhp-hr NOx level, rather than 50%
`at 2.0 g/bhp-hr and 50% at 0.2 g/bhp-hr. The PM
`regulation is at 0.01 g/bhp-hr for either NOx option, or 35 to
`65% tighter than for Euro IV or V (for steady-state and
`transient testing, respectively, including cycle adjustments).
`At 1.1 g/bhp-hr NOx, the 2007 rule is nominally 45% tighter
`than US2004, implying that roughly this level of NOx
`emission control technology can be employed. However,
`US2007 steps to the very tight NOx cap of 0.20 g/bhp-hr in
`2010. The technology chosen to hit 2007, should be
`capable of also hitting 2010. This sets the NOx efficiency
`target ultimately to about 90%, assuming US2004 engine
`technology. Both SCR and LNT have been shown in
`prototype testing to come very close, or actually achieve,
`the 2010 NOx level on pre-2000 engines retrofitted with
`cooled EGR (4, 5). On the PM side, US2007 will be the
`first widespread mandate for filters, although the yet-to-be-
`finalized Japanese regulations for 2005 are pointing in that
`direction. The 2007 Diesel Rule is up for review in 2002,
`and every even year through implementation, to determine
`the state of NOx technology towards hitting the Rule. In
`Europe, just as in the US, the 2008 regulations are
`impacting technology decisions for three years earlier.
`Although the SCR path to hit Euro IV as well as Euro V is
`fairly clear, it is not so with EGR and filters.
`
`Clearly, the role of advanced diesel emission control
`technology is increasing in importance. The technologies
`in one form or another will be on essentially all new diesel
`on-road vehicles in the US, Europe, and Japan, as well as
`several other countries in Asia and perhaps South America.
`In addition, diesel emission control retrofit initiatives and
`mandates are growing worldwide, introducing needs that
`are very different from that for new engines. This paper
`reviews the advances of the pertinent technologies and
`related issues since the last paper by the author, done a
`year ago (6), and does so using representative papers
`
`rather than a complete and comprehensive literature
`review. As in the previous paper, this paper is grouped by
`emissions (nanoparticles, PM, NOx, combinations).
`
`NANOPARTICLE STUDIES
`
`Last year much of the work on nanoparticles from vehicles
`focused on diesel particulates and characterizing the nature
`of the particles and how they are formed and measured.
`The nanoparticle character is described in terms of fine (10
`to 50 nm) “nucleation mode” particles that consist mainly of
`aerosols of sulfuric acid and adsorbed hydrocarbons, and
`solid carbon soot “accumulation mode” particles that
`measure 40 to 200 nm. The accumulation mode particles
`are readily measured and are consistent, whereas the
`nucleation mode particles might vary 2 to 3 orders of
`magnitude, depending on temperature, dilution ratios,
`humidity, and fuels. Preliminary exhaust plume studies
`show that the nucleation mode particles outnumber the
`accumulation mode particles by 100X, and work
`is
`continuing on duplicating those results under laboratory
`conditions.
`
`The key is diluting the hot exhaust gas by upwards of
`1000:1 in one step. Kittelson, et al. (7) described a system
`that accomplishes this and shows some preliminary results.
`Although the shape of the nanoparticle distribution curves
`is not identical to that of exhaust plumes, they show the
`characteristic
`relationship between nucleation and
`accumulation modes. The effects of fuel sulfur levels and
`dilution air temperature are shown in Figure 1. The fraction
`of nanoparticles in the nucleation mode increases when
`going from 10 to 400 ppm sulfur in the fuel, and as the
`dilution temperature decreases. Fuel sulfur gives more
`nuclei precursors, and at the higher temperatures, the
`driving force for condensation is reduced, so fewer particles
`are formed within the specified time.
`
`Figure 1. Preliminary results on a new nanoparticle dilution system that
`dilutes hot exhaust 1000:1 in one step under controlled conditions.
`Nucleation mode nanoparticles increase as fuel sulfur level is increased,
`or as dilution air temperature is decreased. (7)
`
`injection
`fuel
`Although emerging engines have high
`pressures, flexible and multiple injections, and EGR, little is
`known about the effect of these parameters on nanoparticle
`concentrations. Using a 2.1 liter single-cylinder research
`
`BASF-2028.004
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`engine and 50 ppm sulfur fuel, Bertola, et al. (8) showed
`that, with single injections, soot nanoparticle concentrations
`and average size decrease as the injection pressure is
`incrementally increased from 300 to 900 bar, or as the start
`of injection is advanced. (They used a thermodesorber to
`remove condensates.)
` Over
`the range,
`total soot
`concentrations drop an order of magnitude with increasing
`injection pressure, and average soot size drops from 95 to
`50 nm. Peak soot number concentrations drop about 50%
`by advancing timing from about 7 to 14 degrees BTDC
`(before top dead center). Conversely, 22% EGR at 50%
`load and 75% rated speed increases soot nanoparticle
`concentration 6X and average size from 59 to 78 nm at
`1200 bar injection pressure. The trends are similar to
`those recently reported by Raatz and Mueller (9). Figure 2
`shows some typical results. Pilot injections (5%) increase
`concentrations only 20% at 25% load and 60% speed,
`while post injections at 75% load and 87% rated speed
`drop nanoparticle concentrations about 35%.
`
`Figure 2. Increasing fuel injection pressure from 400 to 1200 bar drops
`carbon nanoparticle concentrations up to an order of magnitude. 22%
`EGR has roughly the opposite effect (8).
`
`the particle size
`(10) measured
`Andersson, et al.
`distributions of various light-duty vehicles burning a range
`of diesel, gasoline, and LPG fuel grades. In general, the
`ranges in nanoparticle concentrations are much more
`dependent on vehicle technology rather than the grade of
`fuel burned. Figure 3 shows some results at the 50 km/hr
`steady state condition. The trends shown in the figure are
`typical for all conditions except at 120 km/hr in which it is
`speculated
`the hot exhaust caused desorption of
`accumulated exhaust hydrocarbons from the test system.
`The direct injection engines (diesel and gasoline) are more
`sensitive to fuel grade than the other vehicles, with lower
`PM mass and accumulation mode particles coming with the
`cleaner diesel and gasoline fuels.
`
`(HCCI)
`ignition
`Homogeneous charge compression
`engines show promise for significantly reducing NOx and
`
`Figure 3. Typical particle size distributions measured for various light-
`duty vehicle technologies at 50 km/hr. The trends are representative of
`results at other speeds. (10)
`
`PM to the point of not needing advanced emission control
`to hit any of the regulations on the books. Although
`particulate mass is low, nanoparticle concentrations are
`not. Raatz and Mueller (9) studied nanoparticles coming
`from a 1.8 liter single-cylinder research engine that can be
`adapted
`to
`run with homogeneous or conventional
`combustion. At medium loads, early homogenization in-
`cylinder type HCCI has similar nucleation mode particle
`concentrations as conventional diesel, but much fewer (1.5
`orders fewer) accumulation mode particles. Conversely,
`fumigation (injection of vaporized fuel into the manifold) and
`port fuel hot air homogenization methods have an order of
`magnitude higher nucleation mode particles, but still much
`lower soot particle loads than the conventional baseline.
`
`NANOPARTICULATE SUMMARY
`
`High-dilution rate laboratory set-ups are getting close to
`simulating actual exhaust plume nanoparticle conditions.
`The first results show the large impact of fuel sulfur level on
`the very-fine nucleation-mode particles. Increased fuel
`injection pressures drops nanoparticle concentrations and
`average size, as does earlier injection. EGR and pilot
`injections increase nanoparticles. HCCI engines still have
`nucleation mode nanoparticles on the same order or higher
`than conventional diesel, but the soot or accumulation
`mode particles are significantly reduced.
`
`FILTERS AND PM EMISSION CONTROL
`
`Although diesel particulate filters have been available for
`nearly 20 years, the last several years have seen a
`revolution in the technology. In 2000, the first successful
`filter system for light-duty diesel was introduced and
`described, including exceptional work on the post-injection
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`BASF-2028.005
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`based regeneration system (11). Other reports were
`issued on optimized and alternative filter regeneration
`methods, and the principle of balance point temperature to
`characterize minimum filter regeneration temperatures was
`introduced. Performance in retrofit applications continued
`to be reported. In 2001, the technical literature shifted to
`specifics on filter design properties, such as filter porosity
`and cell geometry performance characterization and
`optimization, and the effects of filter physical and thermal
`properties on durability.
`
`Indicative of a developing
`technology in which major issues are solved first (durability
`and regeneration), new issues are surfaced. In this case
`lube oil ash impacts on filter performance is becoming
`known.
`
`Second-generation light-duty filter systems are emerging.
`The first generation (11) systems incorporated cerium fuel
`borne catalysts to aid regeneration, and used post injection
`of fuel that heated up an oxidation catalyst, which, in turn
`provided enough temperature to periodically burn the soot.
`Indicative of future trends of consolidation, the fuel borne
`catalyst and the diesel oxidation catalyst are replaced with
`a catalyzed soot filter (12). The demonstrated advantages
`of catalyzed filters over the previous system are reduced
`size and complexity (cost), lower soot ignition temperature
`(20 to 60C°), and because there is oxygen storage material
`in the catalyst, CO and hydrocarbon emissions are reduced
`during regeneration.
`
`In both light-duty and heavy-duty filter applications, engine
`management strategies are likely going to be able to supply
`enough heat to accomplish filter regeneration on demand.
`However, for extended operation at very light load and low
`RPM, even the most aggressive engine management
`strategies might not be enough. For these difficult
`applications, Zelenka, et al. reported on burner systems
`(13) and electrical heating systems (14)
`for aiding
`regeneration of filters. Figure 4 shows the outline of the
`burner system for retrofit applications. OEM applications
`might use an air pump. The system can heat cordierite
`filters almost instantaneously with uniform heat and, for an
`11 liter HDD engine, consumes anywhere from 25 to 70
`kW of power depending on load point. Fuel penalties of
`about 2% are estimated. The electrical heating system
`comprises imbedding heating electrodes in a SiC filter. Hot
`Compressed Air Tank
`
`spots are generated and the flame front diffuses from them.
`for a very low effective fuel penalty. A minimum of about 8
`to 9 g soot /liter of filter is needed to generate enough heat
`to make the regeneration self-sustaining. Fuel borne
`catalysts are used to facilitate regeneration.
`
`For years filter durability was thought to be directly related
`to the melting point of the material. Merkel, et al. (15)
`showed that the ash fusion temperature is actually the point
`at which filter durability is compromised in that ash removal
`from the filter becomes limiting. Figure 5 illustrates the
`point. Seven different filter compositions were tested, and
`in most cases the ash sintered to the filter at about 1100°C.
`Perhaps more interestingly and critical, ash fuses to itself at
`900°C, representing the lowest safe peak temperatures for
`filter operation. The investigators developed a relationship
`between
`the peak
`temperature during uncontrolled
`regeneration and
`the amount of soot on
`the
`filter,
`volumetric heat capacity, and thermal conductivity.
`
`thermal
`SiC filters exhibit superb heat capacity and
`conductivity, explaining their robustness in demanding
`applications. The durability is improved even further with
`silicon-containing binder that holds the SiC grains together,
`thus improving thermal conductivity and thermal shock
`resistance (16).
`
`Figure 5. Ash sintering begins at 1100°C for all filter compositions. Filter
`Materials: High-Fe ash; A2: cordierite; G: SiC, B&C: Zr phosphates, D to
`F: alumino silicates. (15)
`
`MV 1
`
`MV 2
`
`Pressure
`reducer
`Mixing
`Chamber
`
`EV
`
`MV 4
`
`MV 3
`
`M
`
`Burner / Filter Unit
`
`LV
`
`ZFG
`
`TB
`
`TvF
`
`PG
`
`TnF
`
`PL
`D+
`5
`30
`Diagnosis
`
`V1
`
`Diesel Fuel Tank
`
`Control Unit
`
`Figure 4. Complete burner system for retrofit applications. OEM applications might use an air pump instead of compressed air. (13)
`
`BASF-2028.006
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`More work was reported on the effect of pore size and
`volume, and filter cell density on filter performance.
`Counter to intuition, Merkel, et al. (17), showed that
`increasing pore diameter does not necessarily translate to
`decreased filter back pressure as the pores quickly fill up
`with soot. They loaded filters with mean pore diameters
`ranging from 3 to 30 µm with model soot. The back
`pressure of fresh filters indeed decreases with increasing
`pore size. However, if even a little soot is introduced, back
`pressure increases for filters with pores larger than about
`12 µm. The authors’ explanation is that if the pores are too
`large, soot can penetrate into the cell wall and easily block
`off passages. If the soot stays on the wall surface, more
`passages are left open, and gas flows easier through the
`developing filter cake. Figure 6 shows the key data. The
`results are for one type of porosity. Pore shape and inter-
`connectivity will likely change the location of the minimum,
`but the principle ought to still play.
`
`Relatedly, soot and washcoat might behave differently, or
`perhaps the pore structure is different, but Taoka, et al.
`(18) demonstrated that for up to 28 g/liter of washcoat
`loadings, increasing the pore diameter from 9 to 20 µm
`decreases the pressure drop through fresh filters. Going to
`40 µm pores does not change
`the back pressure
`relationship. The authors also looked at the effect of SiC
`filter cell geometry, and found that 300 csi filters with 0.012
`inch thick webs have about a 15% lower back pressure
`upon loading than filters with 200 csi and 0.014 inch webs.
`
`Regarding insights into filter regeneration, Opris (19)
`showed that balance point temperature varies with soot
`loading in that heavily loaded cordierite catalyzed filters
`behave similarly to uncatalyzed filters. Opris also warned
`that filter back pressure sensors might not be a reliable
`indicator of soot loading on filters. Under the same
`conditions, filters loaded for 22 hours had the same back
`pressure as those loaded for about 55 hours under
`constant soot loading (2.5X difference in soot on filter).
`Similar results (20) are explained by the nature of the soot
`(dry or wet) and the method of loading (high flow rate vs.
`low flow rate), in that wet soot or soot loaded under high
`flow rates will result in higher back pressure. It is
`reasonable that the packing density of the soot on the cell
`wall can influence flow resistance.
`
`Finally of note, emission control systems are requested
`with as low a back pressure as possible to minimize fuel
`penalty. However, the fuel penalty associated with filters
`varies over a wide range, depending on application and
`engine. Figure 7 shows the results of a simulation model
`that might help explain the discrepancies (21). At any given
`RPM at
`full
`load,
`the simulation shows
`that
`fuel
`consumption increases markedly after a threshold back
`pressure is exceeded. The threshold varies with RPM and
`other factors, perhaps explaining the wide variety of results
`on filter fuel penalties. Pattas, et al. (22) show back
`pressure fuel penalties for a Euro I light duty truck that
`increase about 4.5% for every 100 mbar increase in
`exhaust back pressure. These are similar to the steep part
`of the curves in Figure 7.
`
`Figure 6. Pressure drop of loaded filters is minimized at a pore size of
`about 12 µm. (17)
`
`Figure 7. Full load fuel consumption increases if a threshold filter back
`pressure is exceeded. Simulated results (G-T Power from Gamma
`Technologies) on an Iveco Cursor 8, 7.8 liter, with VGT and pump nozzle
`injectors. (21)
`
`RETROFIT APPLICATIONS
`
`As diesel emission control retrofit applications expand, the
`capabilities and limitations of current systems becomes
`clearer. Also, knowledge on the keys to success expands.
`Mayer, et al. (21, 23) culminated the results of years of
`evaluation of filters retrofit into numerous applications. The
`best predictor of success is the frequency of dwell time at
`various temperature intervals (23). Upon looking at 11
`different applications, the report suggests that catalyzed
`soot filters are only good for the hottest applications (such
`as semi-trailer trucks), fuel borne catalysts work well for
`trucks and motor coaches, and the CRT (continuous
`regenerating trap) has broad application in Switzerland,
`except for some city bus, light delivery, and dump and
`refuse truck applications with low load or low NOx/C ratios.
`
`The New York City Metropolitan Transit Authority city bus
`filter retrofit program has been quite successful and well-
`documented (24, 25). Most surprising in the body of results
`is the performance of the system in eliminating poly-
`aromatic hydrocarbons to the point wherein they are lower
`than on comparable natural gas buses. Figure 8 shows the
`results.
`
`BASF-2028.007
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`contribution to the PM is upwards of 0.0037 g/kW-hr, or
`15% of the total allowed using the European Steady-State
`Test. This level of emissions caused an SCR system to
`lose 27% efficiency over 420,000 km. The investigators
`are recommending fuel lubricated pumps, and lube oils with
`no more than 0.02% phosphorous and 0.25% sulfur to hit
`Euro V PM and NOx requirements using SCR without
`filters.
`
`Regarding cleaning out accumulated ash from filters, the
`method used to clean out filters from Peugeot vehicles
`involves burning out the accumulated soot and then
`cleaning with water and air (28). Zelenka, et al. (14)
`described an
`integrated ash cleaning system
`that
`incorporates the same unit operations in one piece of
`equipment capable of cleaning about 3 to 4 filters per hour.
`
`SUMMARY OF FILTERS AND PM CONTROL
`
`Filter regeneration methods are advancing in that the
`systems are becoming simpler and more integrated. For
`example, catalyzed filters might replace the fuel borne
`catalyst and oxidation catalyst on European passenger
`cars. Filter properties are becoming better understood,
`especially regarding durability, and the effect of pore size
`distribution on back pressure. Some insights into the fuel
`penalty associated with back pressure are emerging.
`Quantification of
`filter and application engineering
`requirements and performance in retrofit applications is
`emerging, thus advancing the field. Lube oil ash impacts
`are being quantified, and filter cleaning procedures are
`being proposed and implemented.
`
`NOx CONTROL
`
`SCR is emerging as the leading NOx reduction technology
`in Europe to hit Euro IV (2005) and Euro V (2008) HDD
`standards. Tuning the engine for low PM, thus eliminating
`the need for filters, results in high NOx emissions and
`better fuel economy. The NOx can be treated with
`nominally 65 and 80% efficient NOx treatment to hit the
`respective regulations. Even after considering the effective
`fuel penalty of the required urea reductant, the fuel savings
`can be as high as 7% relative to a Euro III baseline (2).
`This is indeed an interesting prospect. Given the required
`infrastructure build in Europe to deliver urea, numerous
`reports are emerging on using SCR for the light-duty sector
`as well, although the light-duty NOx regulations in Europe,
`Euro IV in 2005, are generally not tight enough to require
`such advanced emission control. With the emergence of
`ultra-low sulfur diesel fuel in Europe, lean NOx traps are
`becoming an interesting prospect for this sector as well.
`
`As explained in the Introduction, in the US HDD sector
`nominally 45 and 90% NOx reductions will be needed to hit
`the 2007 and 2010 regulations. The heavy-duty engine
`companies are exploring both lean NOx traps and SCR, the
`luxury of which is offered by the mandate of ultra-low sulfur
`diesel fuel. For light-duty vehicles, for the best engines
`today NOx efficiency requirements needed to hit Tier 2
`light-duty regulations vary from about 60% to hit Bin 8
`(loosest final certification level) to about 85% for Bin 5
`
`90
`80
`70
`60
`50
`40
`30
`20
`10
`0
`
`Emissions (ug/mile)
`
`Acenaphthylene
`
`Acenaphthene
`
`Fluorene
`
`2-Me-Fluorene
`
`Phenanthrene
`
`Fluoranthene
`
`Pyrene
`
`TOTAL
`
`OE w/ LSD DPF w/ULSD CNG
`
`Figure 8. Reduction in PAHs in diesel exhaust by the use of filters,
`compared to similar conventional diesel and natural gas buses. (25)
`
`Pattas, et al. (22) evaluated the performance of various
`filter materials and filter locations on a Euro I 2.5 liter IDI
`light duty truck engine. Average filter inlet temperatures
`increase with back pressure, and are about 20C° hotter
`right off the exhaust manifold versus 1 m downstream. Off
`the manifold the variability is regeneration temperature was
`much higher (250-350°C) versus 1 meter downstream
`(300°C). Cordierite filters need higher back pressure to
`regenerate at the downstream location than upstream,
`probably due to the lower temperature. Metallic filters
`(such as those made by SHW – metal wire matrix with
`sintered metal powder) exhibit more frequent regenerations
`at lower back pressure, but have a faster back pressure
`build-up with soot loading.
`
`There is much interest in using fuel emulsions for reducing
`NOx and PM in retrofit applications. Basar et al. (26)
`showed how PM and NOx emissions are generally reduced
`linearly with water additions in the emulsions up to 20%.
`On a 1986 marine engine (Caterpillar 3406B), with 20%
`water emulsions, NOx is dropped only about 8% from 5.94
`g/bhp-hr using 120 ppm sulfur fuel, but PM is dropped 83%
`from 0.46 g/bhp-hr at an injection timing of 26° BTDC. To
`achieve the most effective reductions of both NOx and PM
`emissions, the investigators showed than when injection
`timing is delayed from 26 to 17° BTDC, PM tailpipe
`emissions with the emulsified fuel are still 70% lower from
`the 26° baseline, but NOx emissions can also be dropped
`60%. Although most of these NOx reductions come from
`the injection timing delay itself, the emulsions keep the PM
`down.
`
`LUBRICATING OIL ASH ISSUES
`
`As filter regeneration and design parameters become
`better understood, other issues on filter usage and needs
`emerge. As lube oil ash can clog filters and filters
`eventually need to be cleaned, studies and technology have
`emerged to address the issue.
`
`To understand the extent to which lube oil contributes to
`PM, Jacob, et al. (27) determined that for oil lubricated fuel
`injector pumps, 40 to 70% of the oil ash comes from the
`injector pump, depending on load and speed. The lube oil
`
`BASF-2028.008
`
`

`
`(average certification level) for a vehicle getting 70 mpg
`(mile per gallon). For a vehicle getting 30 mpg, the
`respective required efficiencies are 83 and 95% (29).
`
`Work on non-thermal plasma technology for both light- and
`heavy duty diesel applications is still largely coming from
`the government labs and universities, but, as shown below,
`significant progress is reported.
`
`LEAN NOx TRAPS (LNT)
`
`Last year, reports of LNT technology applied to diesel
`engines were emerging. Preliminary desulfation strategies
`were being reported and
`the
`first results
`for HDD
`applications emerged. Engineers were reporting on how to
`manage the regeneration strategies and drivability. In
`2001, more details emerged on how to design a NOx trap
`system for heavy duty applications; how to regenerate NOx
`traps more efficiently; and very importantly, quantification of
`the sulfur problem and how to desulfate LNT systems.
`
`Before LNT can be applied to full-scale vehicles, many
`fundamental engineering principles need to be worked out
`on the bench scale in the first steps of development.
`Michon, et al. (30) conducted comprehensive work on a
`single-cylinder, supercharged 1.64 liter research engine.
`After establishing that periodic rich conditions with and
`without EGR would likely not adversely impact engine
`durability, as indicated by peak cylinder temperatures, they
`began quantify